The present invention is generally related to a method and composition for removing photoresist and, more particularly, is related to a method and composition of removing photoresist from a silicon substrate using relatively nontoxic and noncorrosive materials.
The continuous reduction of dimensions in microelectronic devices and integrated circuits results in more stringent requirements for acceptable levels of various contamination and organic residues on the wafer surface. New device generations lead to the use of new materials and increased number of process steps. There has been a drive in recent years to reduce the use of the enormous volume of de-ionized water used in wafer rinsing steps in order to minimize the cost-of-ownership. Cleaning methods, such as the RCA clean or Pihranna etch techniques attempt to accomplish removal with aqueous phase chemistry. The RCA technique uses baths of hydrogen peroxide/ammonium hydroxide/de-ionized water and hydrogen peroxide/hydrochloric acid/de-ionized water and de-ionized water rinses to clean surfaces. However, this technique and others have various limitations; specifically, they are not compatible with vacuum transfer, they have difficulty removing high dose ion implanted photoresist, and they produce toxic and corrosive waste.
The photoresist stripping process can be costly as well as a source of various production problems such as contamination and device layer damage. For photoresist and ion implanted photoresist removal there are two main technologies, plasma treatment and liquid stripping techniques. Plasma treatments utilize glow discharges that typically contain oxygen, hydrogen, and fluorine and operate at temperatures above 100xc2x0 C. to maximize reactivity. In contrast, liquid stripping techniques make use of solvents or aqueous phase strippers. Solvents often remove material through a dissolution mechanism. Aqueous phase strippers are water-based with various chemicals added to increase chemical reactivity and solution strength to achieve dissolution and degradation of the photoresist.
Currently, plasma ashing of photoresist using downstream based plasmas has received allot of attention mainly due to the high stripping rates (1-2.9 xcexcm/min) that can be achieved by this method. Some of the ashing methods used include barrel ashers, microwave plasmas and RIE configurations. However, this method is very expensive and can cause damage to film surfaces and devices because high-energy particles impact the wafer surface. Another problem that is often encountered in plasma stripping is that plasma exposure might make photoresist residues harder to remove. In addition, plasma ashing can cause metal (e.g., iron) and alkali ion (e.g., sodium and potassium) contamination that results in reduced device lifetimes, reduced reliability, and threshold shifts. The source of these contaminants is frequently the photoresist material.
Wet stripping methods that use organic solvents and reactive aqueous strippers are the most common method of stripping in front end of line (FEOL) processes. As in the case of dry resist stripping, there are drawbacks associated with wet stripping. For instance, stripping solutions are generally toxic and corrosive, which results in high disposal and handling costs. Even the addition of ozone to aqueous baths, which has been used to remove resist material (Kashkoush et al., Materials Research Society Symposium Proceedings, Vol 477, 1997, p. 173.), can result in toxicity concerns. (Crowl and Louvar, Chemical Process Safety: Fundamentals with Applications, Prentice Hall, 1990, pp. 42-44). Often, a residual layer remains on the wafer surface, which may require extra steps to rinse the surface. Stripping solutions also lose potency with time and accumulated contamination in the solutions can be a source of contaminating particles. Another method of stripping photoresist uses acetone, a liquid that often has high levels of impurities. Some stripping processes under investigation use de-ionized water with isopropyl alcohol and potassium fluoride additions. (Ojina et al., Journal of Electrochemical Society, Vol. 144, 1997, p. 4005) However, the use of stripping methods using potassium fluoride makes the waste solution disposal costly and more difficult. All of the above stripping methods result in waste streams, which require careful and often costly disposal methods.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
One embodiment of the present invention is a liquid cleaning composition for removal of photoresist including an aliphatic alcohol. Generally, the alcohol is of low-molecular weight and contains fewer than six carbon atoms. Preferably, the alcohol is isopropyl alcohol. The temperature conditions for using the present invention are generally less than about 100 degrees C. The pressure conditions for using the present invention are generally less than about 100 pounds per square inch.
Another embodiment of the present invention is a liquid cleaning composition for removal of photoresist including an aliphatic alcohol and an aqueous base. Generally, the alcohol is of low-molecular weight and contains fewer than six carbon atoms. Preferably, the alcohol is isopropyl alcohol, while the aqueous base is ammonium hydroxide. The temperature conditions for using the present invention are generally less than about 100 degrees C. The pressure conditions for using the present invention are generally less than about 100 pounds per square inch.
A further embodiment of the present invention is a method for the removal of photoresist from a substrate. A layer of photoresist is put upon a substrate. Then the coated substrate is exposed to an aliphatic alcohol. Generally, the alcohol is of low-molecular weight and contains fewer than six carbon atoms. Preferably, the alcohol is isopropyl alcohol. The temperature conditions for using the present invention are generally less than about 100 degrees C. The pressure conditions for using the present invention are generally less than about 100 pounds per square inch.
Still a further embodiment of the present invention is a method for the removal of photoresist from a substrate. A layer of photoresist is put upon a substrate. Then the coated substrate is exposed to an aliphatic alcohol/aqueous base mixture. Generally, the alcohol is of low-molecular weight and contains fewer than six carbon atoms. Preferably, the alcohol is isopropyl alcohol, while the aqueous base is ammonium alcohol. The temperature conditions for using the present invention are generally less than about 100 degrees C. The pressure conditions for using the present invention are generally less than about 100 pounds per square inch.
Other systems, methods, features, and advantages of the present invention are or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.